Gun bore measuring device



Aug. 19, 1952 D. H. NEWHALL 2,607,128

GUN BORE MEASURING DEVICE Filed Jan. 29, 1948 2 SHEETS-SHEET 1 iiifill 70 LIMIT JWITCW grwcmtm B m-11:1 H NE-w1-m11,

Aug. 19, 1952 Filed Jan. 29, 1948 D. H. NEWHALL GUN BORE MEASURING DEVICE 2 SHEETS-SHEET 2 P0 WEE Patented Aug. 19, 1952 j UNITED STATES A T OF Claims.

The inventiondescribed herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon-J This invention relates to a device for measuring the bore diameter of gun tubes by the use of electric strain'gages and an electrical recording device to automatic'all-yrecord the deviations ofthe bore diameter.

3 I Measurement of bore diameters of firearm barrels-has been done in the past by an instrument called'a star gage. Such instrument wasmanipulatedmanually to expand an opposed pair of 1 feeler arms which engaged corresponding opposed lands or grooves and the-reading of the bore diameters was then visually noted and likewise manually recorded. In the case of small arms barrels such a procedure while tedious was not too arduous although quite-slow. In the case of gun tubes of larger caliber, star gagingv of such a tube by conventional measuring means was definitely a slow laboriousprocedure and at best only a comparatively small. number of 'bore measurements could be tak'en'in view 'of thegreat amount of time involved in taking more frequent measurements. 'Then'too', 'theaccuracy of the bore diameters as obtained by conventional methods was'dependent entirely upon the skill of the person manipulating the gage.

Accordinglygit is an .object of this invention to provide a device. whereby. the inside diameter of .gun tubes can. be rapidly and accurately measured.

Another objectlof this invention is to provide a device a tojautomatically measure and record.

an infinite number :of bore measurements.

Still. another object .of. thisinvention is to provide a device for automatically. 1 measuring a plurality of lands'and/or groovessimultaneously. A furtherobjectof-this invention .isto provide a .device for accurately and automaticallymeasamended April 30, 1928; 370 0. G. 757) uring the deviation in the normal height of the land of a firearm barrel from the. adjacent groove; I y

The specific nature of the invention as well as other objects andladvantages; thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings in which:

v ;Fig. 1 ;is an enlarged longitudinal sectional view of the measuringhead showing the arrangement of the strain gages therein. Fig. 2 shows'a longitudinal sectional view of a gun tube illustrating the general arrangement 50f thefbore measuring device when measuring the bore diameter ofgun-tubes'.

Fig. 3 is a fragmentary member of the driving mechanismshowing the manner of slidably mounting such mechanism.

Fig. 4 is a cross sectional view taken alongthe line ie-lot Fig;'1. r

Fig.5 is a schematic diagram of thc wiring circuit utilized in the recor'dingdevice in coniunction with the measuring he'a'd-ofthis inven- 11 v This invention essentially consists of: utilizing electric strain members securedto cantilevered beams mountedin a measuring head which in turn is inserted in the bore of a g'u'n tube. The change in resistance of each of such strain members, produced by flexing of the beams, is recorded on an electrical recording device." Such recording device, calibrated toread the bore diameter directly, produces a graph on which is automatically recorded an infinite number of measurements within the gun tube. The head containing the electric strain members is traversed through the bore' of the gun tube by means of a motor driven traversing mechanism. Accordingly, there is shown in Figs. 2 and 4 a gun'tube H] which is preferably supported in a horizontal position in any suitable fashion. Tube It is provided with a muzzle end M, a bore l2 and within the bore l2 grooves25 and lands 2% are provided. Ameasuringhead H is adapted to be inserted in bore [2 ofguntube Iii. A driving mechanism l3 isprovided to traverse head H through bore l2 in a manner that will belater explained. Driving mechanism'lil is preferably mounted on muzzle end 14 of tube iii.

Measuring head H comprises a body portion IS, a pair of cylindrical bearing plates It; one each of such plates being securedto opposite endsof body l5,;an d apair ofoppcsitely disposed strain gages ll mounted 'in a manner te be-later described. 'Body15 is, asubstantially cylindrical portion i5 by screws fi l vv'hich engage suitable threaded holes 22 providedlin flange it. Right hand bearing plate 16, as shown in Figl, is provided with an axially disposed .integralboss 2t and. a .clevis 28 is rotatabl'yI's'ecured to boss 24 by anut Z'I. 1"

Approximately in the center of body portion I5 there is provided an enlarged diameter portion 3i substantially cylindrical: but provided with diametrically opposed milled flat surfaces detail view ofthe base 32. On the left end of each of the flat portions 32 there is provided an upstanding bifurcated lug 33. Adjacent the right end of enlarged portion 3| there is provided an integral flange 34 and adjacent flange 34 there is provided a hub 35 of substantially lesser diameter than flange 34.

A cylindrical bearing member 36 is mounted on hub 35-, a cylindrical recessv 31 being provided in the left face of such bearing member as shown in Fig. 1 to permit such bearing member to be placed adjacent flange 34. An axial hole 38 provided in bearing member 36 permits such bearing member to snugly fit on hub 35. A plurality of suitable screws secure bearing member 36 to flange 34.

It is obvious that bearing member 36 must be assembled to body portion l prior to assembling right hand bearing plate |6. Itis also obvious that the bearing plates |6 and bearing member 36 have the same outside diameter and such diameter is of a size such as to permit the whole assembly to readily slide within the bore I2 of gun tube ID. A pair of opposed beam clearance slots 4|] are provided in bearing member 36 which communicate with recess 31 as shown in Fig. l k

for a purpose to be presently described.

Strain gages H are mounted within the bifurcation provided by lugs 33. Each strain gage l1 comprises a pair of cantilever beams 4i and 42 placed one above the other and separated by a block 43. Beams 4| and 42 are secured to enlarged diameter portion 3| by screws 44. A longitudinally slidable wedge block 45 is actuated by a screw 46 threaded into a suitable hole 41 in bearing member 36. Such block is bifurcated in order to surround screws 44 so that the sloped surface of block 45 can engage a block 48 placed underneath cantilever beam 42 and cooperate with a corresponding slope on such block to raise or lower beams 4| and 42. The free ends of cantilever beams 4| and 42 project towards the right, as shown in Fig. 1 into slots 49.

A guide button 49 is secured to the free end of beam 4| and is provided to engage either a groove or land in bore I2. This will be explained in more detail later. A button 59 is provided on cantilever beam 42 opposite button 49 and engageable by button 49. On each side of beam 42, that is, on the upper and lower sides of such beam, there is provided an electrical strain member5| and 52. Strain members 5| and 52 are connected to a self-balancing bridge 14 as shown in Fig. 5 and the function thereof will be later explained.

Buttons 49 are provided with a contact end of suitable shape to properly engage either the land or the groove of tube I9; In order to insure that button 49 will remain in engagement with the same groove or land in tube ||l, guide keys 53 and 54 are provided on opposite faces of bearing member 36. Such keys comprise a plate member 55 having a projecting finger-like lug 56 thereon. Lug 56 is shaped to enter a groove provided in the bore |2 of tube It] and such lug is preferably bifurcated to provide a spring-like action in order 4 contact with either the groove or land as may be desired. The height or the distance from the center of head I to button 49 is readily adjusted by means of Wedge 45. Such adjustment is provided to permit the button 49 to ride in the groove or on top of the land. As may be appreciated,

: there is a substantial difference between groove diameters and bore diameters so that such adjustment is necessary to avoid putting undue strain on the beams 4| and 42.

The outside beam 4| is provided to eliminate the friction load on beam 42 to which the strain members are attached. The friction load producedby dragging head I through bore |2 of gun tube 10 is taken up by the outside cantilever beam 4|. Such beam flexes with any change in diameter and produces a corresponding flexing movement on beam 42. As beam 42 is flexed by the variations in the diameter of the bore, strain members 5| and 52 change in resistance in proportion to the deflection of such beams. In the preferred form of this invention, four such strain members are provided, two of which produce an increase in resistance While the other two produce a decrease in resistance as the beams are flexed. r p g Head H is arranged to be pulled through bore |2 of tube ID by means of traversing mechanism l3 as will now be described. A bracket 59 is provided to support traversing. mechanism l3. Bracket 59 comprises a base-like member 69 which is utilized to support a motor driven gear reduction unit 62. Unit 62 is driven by a synchronous electric motor 6|, the purpose ofrwhich will be later described. A web 63 is provided on the underside of bracket 59-for stiffening purposes. On the left end of bracket59 as shown in Fig. 2, there is provided a semi-cylindrical mounting member 64 which is adapted to surround onehalf of the muzzleend |4of tube I 0. A stop plate 65 is welded to the front side of mounting member 64 as shown in Fig. 2 fora purpose to be later described." A web member 66 is provided on top of base 69 which is welded thereto and to plate 65 also for stiffening purposes.

A pair .of clamps 'H- are provided which are secured to mounting member 64 by means of bolts I2. Clamps 7| surround the top half of muzzle l4 and are provided to, secure bracket 59 to muzzle l4. Gear reduction unit 62, with motor 6 I attached thereto, is slidably mounted on the right end of base member 60 and is secured thereto by bolts 61. Bolts 61 are passed through slotted holes 68 in base member 69 to provide limited longitudinal movement of gear reduction unit 62. A pair of stop members'69'ar'e provided on top of base member 60 and a'spring 79 is placed between each stopv member '69 and the :base of gear reduction unit 62 to return such unit to its 7 normal position as will. be presently explained.

The longitudinal position of'gear reduction unit 62 on base member 69 may be adjusted bymeans of screws 8|. Such screws are horizontally disposed in suitable lugs 82 secured to the right end of base member 69.

'A limit switch 86 is secured to base member 66 adjacent the left hand edge ofgear reduction unit 62. A contact plunger 93 projectingfrom limit switch 86 is arranged to contact'asuitable stop 84 secured to gear reduction unit 62 when such unit is moved to the leftasshown inFig. 2 and as will be'presently explained.

A sprocket .85 is secured in aconventional mannor to' gear reduction; unit 62..I'Connection between measuring head andgearl reduction unit or achain 53. one end of such chain is secured;toiclvis 28 and the other a schematic diagram illustrating the circuitof a conventional automatic recording device utilized in conjunction with measuring head H above described. In this device the electrical signal picked up byft h'e cantilever beam 42 is introduced to a conventional power unit 53 Where such v signal is amplified and then the amplified signal is referred to a self-balancing bridge circuit id. A recording mechanism 75 is provided which comprises apen 16; a solenoid motor TI, and a balance bar 18, one end of which is connected to bridge circuit 14 and the other end to; motor TI. Unbalancing of bridge circuit '54 actuates solenoid motor 17 to effect, movement of pen le. A chart I9 is associated with pen I6 and is arranged to run under the pen #6 with a speed proportional to the traverse of measuring head II Such is accomplished by means of 'a motor drive (not shown) which is synchronized with motor BI. In the preferred form of this invention a length of two feet of chart 19 represents the profile of gun tube Ill from the breech to the muzzle which in this preferred embodiment is equivalent to 232' inches. A centerline 8% is providedon-ehart I9 and'pen I6 is adjusted to rest on such line when button 49 is on the nominal .diameteric dimension of the un tube.

As the measuring head I I is traversed through bore I2 of tube Iii by motor 6|, any increase or decrease in the diameter of bore I2 flexes beams 42 due to the contact of buttons 49 with buttons at a reement nseam,

thereby changing the resistance of strain members Si or 52 or both which produces an electrical signal and causes a displacement of pen I6 from the centerline 80 of chart IS an amount proportional to the change in diameter recognized by cantilever beam 42. As measurin head II is traversed along the bore, guides 53 and 54 impart a rotary movement to head II in conformance to the helical lead of the grooves provided in bore I2 thereby keeping buttons 49 on the groove or land as the case may be.

It is thus apparent from the foregoing description that there is here provided a device to automatically measure and record an infinite number of interior bore diameter measurements which substantially eliminates all manual-operation. Further, this invention provides a device wherein such measurements can be made with much greater rapidity and a vastly higher degree of accuracy than by any other known prior art. It is also desired to point out that this device can be used for the measurement of any interior bore or other opening where the sides are substantially parallel. vention can be readily broadened and yet lie within the scope of this invention to record the profile of any angularly shaped hollow member The use of this in-V and aetbmaeeau recorded.

aarla ikewise "Queer-rem desert: any eynriarical object can be resent; ecbifded. Automatic r'ecording of an average diameters easily achieved by the use of a pic'ral'fityor .7 In addition, multiple independent measurements of diam:- eters at vanb'us'a gmar positions with'respect to the centerof the tube may be simultaneously Itis;nether detects same as ear iestrangement shown herein is such that a relatively loose fit of measuring head II within bore, I2

"cause no error in tlieprecision or accuracy of t m afse m m w s i he fact arg ns HI and 4 2 are preloaded and therefore any devia tion tro m the linear transverse movement of such headfwithin tube canses an increase in thedefiection of one pair of beams and an equal d cre e i e e' 'iio 9 t eo Pai P ams h n e he alan ed thee a bri remains constant exceptfor changes in diameter. It is r th rem reet th t-" ub ta ti .t a on the bearing portibns of the measuring head can be tolerated as long as the beams are properly i il fimd- IJQl mLQ 7.; j .7

In a ra us ar mew-i decrease in the boredian etei theiincre ase or a tube, the combination of a diametrically opposedpair Yof fiexibly mounted st rain, gages, and a cantilever beam ou tedin ux siti n- Wit each of said se said beam being alsomounted so that the free end thereof simultaneously contacts the interior bore surface of the tube; and the free endof said juxtaposed strain; gage 'wherebyy-the flexing movements of said beams produced by an increase ordecreasein the bore diameterofthe tube are correspondingly transferred to said strain gages for indicatingthe' degree of .fiexureof said beams relative ,tothe-initial position thereof.

2.. Inapparatus adapted to be traversed V H through -.a. tube: for measuring-the increase; or

decrease in :the bore. diameter .thereof,; the: combination of a diametrically opposed pairof first cantilever beams a straimelement fixedly secured on either side ofsaidfirstabeams adjacent the area ofzflexure thereof; a second cantilever beam interposed between the interior bore sur--- :face of the :tube and each *ofis'aid first %beams, and

projecting means fixedlysecured to the free ends of said second beams and arranged to simultaneously contact the interior bore surface of the tube and the free end of each of said first beams whereby the flexing movements of said second beams produced by increases and decreases in the. bore diameter of the tube are directly transferred to said first beams and actuate said strain elements in accordance with the degree of radial movement of said projecting means to indicate the relative changes in the bore diameter of the tube.

3. In apparatus for measuring the changes in the bore diameter of gun barrels having a plurality of helical lands and grooves, the combination of a measuring head adapted for helical traverse through the gun barrel, a pair offirst cantilever beams mounted on opposite sides of said measuring head, an electrical strain sensitive element fixedly secured to either side of each of said first beams adjacent the area of flexure thereof, a second cantilever beam interposed between the interior bore surface of the barrel and each of said first beams, a contact button projecting substantially at right angles from either side of the free end of each of said second beams,

said first and second beams being equally preloaded whereby said contact button is maintained in simultaneous contact with the-free end of said first beam and either a land or groove in the barrel despite changesin the bore diameter of the'barrel, and meansassociated with said strain elements for continuously indicating the diiferences between the degree of flexing of each of said second beams for determining the relative increases and decreasesin thediametrical distance between opposite lands or grooves in the barrel.

4. Apparatus for'measuring the increases and decreases in the diametrical distance between an opposite pair of helically disposed lands in a rifled gun barrel comprising, in combination, a measuring head, means for helically traversing said head through the bore of the barrel in accordance with the helical path of the grooves formed by adjacent lands, a pair of electrical strain gages flexibly mounted on opposite sides of said measuring head, a cantilever beam mounted in said headin juxtaposition with each ofsaid strain gages, means on the free end of each of said cantilever beams for transferring to said strain gages the degree of flexing produced by increases and decreases in the contour of the interior bore surface of the barrel, means for radially adjusting each combination of said cantilever beams and said strain gages in accordance with the predetermined land or groove to be measured and means for continuously indicating the relative electrical resistance produced in said strain gages by the flexing thereof for measuring the changes in the diametrical distance between opposed pairs of lands or grooves;

5. Apparatus for continuously measuring the increases and decreases in the diametrical distance between an opposite pair of helically disjecting substantially at right angles from either side of the free end of each of said second beams and normally arranged to protrude beyond the outer surface of said measuring head, said first and second beams being equally preloaded whereby said buttons are maintained in simultaneous contact with the bottom surface of the barrel groove and the free end of said first beam, means for traversing said measuring head through the barrel, means for imparting helical movement to said measuring head in correspondence to the helical path of thegrooves in the barrel whereby said contact buttons are continuously engaged in opposite grooves, means for radially adjusting the degree of protrusion of said contact buttons from said measuring head, and means for continuously indicating the relative electrical resistance produced in said strain gages by the flexing thereof for measuring the increases and decreases in the diametrical distance between an opposed pair of gun barrel grooves.

DONALD H. NEWHALL.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 1,912,618 Bryant June 6, 1933 1,946,924 Allen et al Feb. 13, 1934 2,099,896 Kinzel Nov. 23, 1937 2,208,635 Johnson July 23, 1940 2,219,708 Kruse Oct. 29, 1940 2,239,811 Cuppers Apr. 29, 1941 2,239,981 Terry et a1 Apr. 29, 1941 2,316,975 Ruge Apr. 20, 1943 2,325,299 Bench et al July 27, 1943 2,369,909 'Mestas Feb. 20, 1945 2,439,595 Cooke Apr. 13, 1948 2,487,681 Weisselberg Nov. 8, 1949 2,495,797 Whitlock et al Jan. 31, 1950 2,547,647 Levesque Apr. 3, 1951 FOREIGN PATENTS Number Country Date 565,504 Great Britain Nov. 14, 1944 OTHER REFERENCES Journal of Scientific Instruments, Nov. 1945,

page 219. 

